1. Field of the Invention
The present invention relates to the use of a cryophotonic panel or lamp for providing back lighting for a sign. In particular, the present invention relates to the use of a cryophotonic panel or lamp together with a translucent retroreflective sheeting in order to provide sufficient back lighting for a sign to be seen at night or during dimly-lit times during the day.
2. Description of the Related Art
Traffic signs provide information that is useful for a driver of a vehicle. For example, traffic signs may provide an indication of an upcoming exit, a maximum safe vehicle speed, or the like. During the daytime, traffic signs are readily visible to a vehicle operator. However, traffic signs also need to be visible at night or during dark periods of the day (i.e., such as during a rainstorm), and something other than sunlight has to be used in order to make such signs visible to the vehicle operator.
Accordingly, several different types of signs have been manufactured so as to make traffic signs visible at night, as well as during the daylight hours. One such conventional traffic sign is disclosed in U.S. Pat. No. 2,910,792, issued to H. C. Pfaff, Jr. Pfaff discloses a highway sign that has an electrically energized luminescent material containing layer. The layer includes light reflecting members fixed or embedded onto a surface thereof. When the luminescent layer is excited with alternating or high frequency current, particles in the layer become luminescent. When headlights of a vehicle provide light rays that impinge on the light reflecting members, those members reflect the light rays back, so as to provide a lighting capability for the sign. The luminescent material layer is secured to a metal base plate by baking or firing, and no provision is provided for protecting that layer from problems associated with neighboring components, such as the light reflecting members.
U.S. Pat. No. 3,510,976, issued to R. F. Pauline et al., discloses a traffic sign that has a reflective face by virtue of beads disposed on a surface thereof. An electric bulb is disposed behind the reflective face, inside the sign itself. The electric bulb provides light that passes through the reflective face so as to provide lighting for the sign when there is not enough ambient light (such as from headlights of a car) that can be reflected off of the reflective face of the sign to provide the necessary lighting for the sign. However, with this system, whenever the light bulb burns out, a repairperson must replace the light bulb with another light bulb. This may cause a problem in that a road has to be blocked off for a particular amount of time during the bulb replacement, especially when the sign is located above the road.
U.S. Pat. No. 4,005,538, issued to C. Tung, discloses an internally illuminated retroreflective sign that has an array of tubular light bulbs that provide the internal light source when not enough reflective light is available to make the sign visible to a vehicle operator. The tubular lights bulbs may have to be replaced from time to time, which may involve a closure of a road, if the sign is located above the road and thus a repair truck must block the road during the time the repair is being made. Also, an undesirable shadowing effect may be created by the use of the tubular light bulbs disposed behind the retroreflective sheeting.
3M has also utilized something known as OLF, or optical lighting film, so as to provide a light source from a location separate from the sign itself, such as in a box located on the side of road for a sign hung above the road. As in the Tung et al. reference, however, the separately located light source uses incandescent bulbs or the like, and is prone to fairly frequent replacement.
U.S. Pat. Nos. 5,300,783, and 5,315,491, issued to A. Spencer et al., disclose the use of a retroreflective material having a prism-like surface, with an electroluminescent lamp disposed within a central region behind the retroreflective material. The electroluminescent lamp is composed of a flexible material, and is not protected from the internal atmosphere in the central region. This may cause the lamp to breakdown over time, requiring relatively frequent replacement.
Great Britain Published Patent Application GB 2 099 628A discloses a device having a mirror with an electroluminescent element mounted its rear face. The device is used as an interior rear view mirror for a vehicle, and the device does not provide any protective capability for the electroluminescent element.
For all of the signs/reflecting devices discussed above, there is a problem in that the life span of these devices is limited due to the exposure of important components to the atmosphere and/or neighboring components.